Fiber optical communication systems are in widespread use, and it is important that such systems have optical receiver subsystems that can be manufactured efficiently and inexpensively, and which do not compromise the high speed capability of the communication system.
One aspect of optical receiver design involves minimizing parasitic inductance that arises, in high frequency operation, when conductor length (such as circuit wiring) is relatively long. To control parasitic inductance, the length of electrical conductive path between the connection points for the components has to be minimized in order to reduce the inductance effect.
Also, free space passive alignment at the receiver between a photodetector (typically, a photodiode) and the distal end of the optical fiber, for low cost assembly, is a challenge in a system without a lens, due to the divergence nature of the light exiting from the optical fiber. Direct coupling that allows the surface of the optical fiber to mate to the surface of the active area of, for example, a back-illuminated photodiode, is desired to optimize the light coupling efficiency. However, the back-illuminated photodiode requires the chip to be flipped and attached on an extended electrically conductive path for wire bonding from a transimpedance amplifier (TIA). This increases the conductive path length from photodiode to TIA, resulting in additional inductance. Moreover, the direct coupling design requires a clearance of an area equivalent to at least the fiber ferrule diameter, making the design to shorten the conductive path between TIA and the photodiode become a challenge when photodiode and the TIA are mounted on the same plane.
Furthermore, if all the components are incorporated on the same plane, the area required per unit substrate increases substantially, and this can greatly increase the unit cost of the receiver subassembly.
It is among the objectives of the invention to overcome these and other problems and limitations of prior art equipments and techniques, and to provide optical receivers and techniques that exhibit attributes of improved manufacturability and operation.